Lithium compound-containing electrochemical cells and batteries including such cells are modern means for storing energy. They exceed certain conventional secondary batteries with respect to capacity and life-time and, in many times, use of toxic materials such as lead can be avoided. However, in contrast to conventional lead-based secondary batteries, various technical problems have not yet been solved.
Secondary batteries based on cathodes including lithiated metal oxides such as LiCoO2, LiMn2O4, and LiFePO4 are well established. However, some batteries of this type are limited in capacity. For that reason, numerous attempts have been made to improve the electrode materials. Particularly promising are so-called lithium sulfur batteries. In such batteries, lithium will be oxidized and converted to lithium sulfides such as Li2S8−a, a being a number in the range from zero to 7. During recharging, lithium and sulfur will be regenerated. Such secondary cells have the advantage of a high capacity.
Sulfide materials of different compositions and nature are known to be lithium-ion conductors (e.g., Li2Sx/P2S5 glasses, Li2Sx/P2S5-derived glass ceramics, Li7P3S11, thio-LISICON, oxysulfide glasses). However, such materials may suffer from issues such as low stability against liquid organic electrolyte solutions, insufficient stability against metallic lithium or high voltage cathode materials, extreme sensitivity to moisture and/or air, and/or an intrinsically low ionic conductivity.
Accordingly, improved lithium-ion ionically conductive compounds are needed.